1. Field of the Invention
The present invention relates to an improved alpine snow ski, and a method of making the same, effectively utilizing high strength steel or equivalent metallic material.
2. Background Art
Over the last several decades, the techniques in the design and manufacture of snow skis have undergone considerable improvement and become substantially more sophisticated. Prior to 1950, skis were commonly made of high quality wood, with metal edges being attached to the lower side edges of the ski to improved the turning capability of the ski without excessive slipping, particularly on an icy surface.
In the early 1950's, there was the introduction of a ski (manufactured by the Head Ski Company, U.S.A.) having a wood core to which were attached upper and lower aluminum sheets. While this design experienced a large degree of acceptance and provided many advantages over wooden skis, there were some shortcomings. One of these was that the design then available had excessive weight, making them more difficult to run than the wooden predecessors.
A ski of this general design is illustrated in U.S. Pat. No. 3,095,207, Head, where there is described a ski having upper and lower plates made of an aluminum alloy, and a core material made of plywood. In the particular configuration as shown in this patent, the edges of the ski are formed of steel strips that are placed in slits or grooves that are cut or milled in the lower aluminum alloy plate.
Accordingly, there were various design efforts to improve the performance of this aluminum sandwich ski, as described above, and one such approach was to add one or more rubber layers to the sandwich or laminations which made up the ski to dampen the vibrations.
In the early 1960s, skis utilizing fiber reinforced plastic as the main structural material made their appearance. One of the main advantages of this material is that it has very high strength, both in compression and in tension, relative to the density (i.e. weight per unit of volume) of the material. The earlier designs were in the nature of a laminated structure, where there was a sandwich of fiber reinforced plastic and high quality wood.
At a later time (i.e. around the mid 1960's or shortly thereafter), skis having a box-like structure made of fiber reinforced plastic became more prevalent. Also, during approximately that same time period, skis having a honeycomb core structure made their appearance.
The introduction of the foregoing "aerospace" material into ski designs was motivated by the desire to create a ski of lower weight than the Head-type aluminum laminated skis, and thereby improve the turning properties of the ski.
As we approach present day ski designs, it appears that the evolution of the design of skis has been such that many earlier designs have, in a structural sense, given way to only a few current designs. Further, the design parameters have been channeled so that in terms of structural characteristics, the present day skis lie within a relatively narrow range of flexural stiffness, torsional stiffness, weight and strength. These have in a sense set the standards by which any new ski design must be measured.
Most any ski that is widely available today can be classified into one of three categories as to its principal structure: (a) aluminum sandwich structure, (b) fiber reinforced plastic, or (c) fiber reinforced plastic and aluminum combined. The wide variety of available models differs as to the type of core, edge and geometric design (i.e. side cut (contour) and stiffness distribution), but nonetheless, each model can be placed into one of the three groups. Despite the differences of core type and edge design within each group, there is a strong similarity in fundamental ski properties within each of the three groups. This is true largely because ski designs in the three groups have evolved to a point where a very narrow range of ski weight and stiffness is found to be acceptable to the ski market.
First, with regard to flexural stiffness, EI, where E is Young's modulus and I is the second area moment of the cross-section, this generally must lie within a range of about 5000-10,000 pound inches squared (lb-in.sup.2) at the extreme ends, to about 250,000 lb-in.sup.2 at the ski center (for a full length ski). The distribution of EI between these values varies with the type of service for which the ski is designed and determines to a large extent the "feel" of the ski.
Second, the torsional stiffness of the ski must be greater than a certain minimum. This is necessary so that the edge of the ski can hold to the underlying surface adequately when a turn is being executed.
Third, the weight of the ski should not be more than that of skis which are widely available at this time, these being the basic aluminum, fiber reinforced plastic, or combination of the two. This is primarily because both weight and flexural stiffness determine the dynamic response character of the ski, and since the allowable stiffness of skis is determined by skier weight and type of service, the ski weight is limited within a small range since the dynamic response expected by the market is largely predetermined.
Fourth, there is the necessary characteristic of basic durability, the most important part being resistance to permanent bending, called "yield strength".
In addition to the ski designs which have been manufactured commercially and found at least some degree of acceptance in the marketplace, there have been a large number of proposed designs, some of which have incorporated metal to form the main, or one of the main, structural elements. A number of these have appeared in the patent literature, and the following are noted as examples of these.
U.S. Pat. No. 1,552,990, Hunt, shows a ski that is made from sheet metal. The top sheet metal piece has two downwardly extending flanges, and these overlap with, and are soldered to, upwardly extending side flanges that are made integral with a bottom metal sheet. In some configurations, there are vertical webs or reinforcing members extending between the top and bottom sheets.
U.S. Pat. No. 2,038,077, Haglund, shows a ski where upper and lower strips of metal are bonded to one another, with no space between the two strips. The patent states that other laminations could be provided.
U.S. Pat. No. 2,743,113, Griggs, relates primarily to a metallic running edge for a ski.
U.S. Pat. No. 2,971,766, Holley, shows a wood ski where there are metal edge strips.
U.S. Pat. No. 3,095,207, Head (mentioned earlier herein), shows a ski having a wood core bonded to upper and lower aluminum alloy plates. At the side edges of the ski, there are surface strips 16 made of resin.
U.S. Pat. No. 3,134,604, Aublinger, is another example of a configuration of metal edges that are applied to the lower edge portions of the ski.
U.S. Pat. No. 3,151,873, Riha, relates to a metal ski where there is a top metal section and a lower U-shaped metal section having what might be described as side walls with a corrugated or undulating configuration. The top metal section is a flat plate. The U-shaped metal section has the upper arms or walls of the "U" curved outwardly to join the edge portions of the top plate. Among the various advantages alleged, it is stated that the side walls impart a sufficient flexibility to the ski because the side walls afford relatively small resistance to bending of an edge, with the undulations and the provisions of the edge strips insuring a sufficient resiliency and shock absorption.
U.S. Pat. No. 3,208,761, Sullivan et al, shows a ski having upper and lower metal parts. The lower part has two upstanding side walls and these are made with grooves which match with mating grooves in the top wall. The patent also states that the upper and lower pieces could be reversed, so that the juncture would be at lower edge. The interior of this structure is filled with a foam.
U.S. Pat. No. 3,272,522, Kennedy, shows a composite metal and plastic ski. Specifically, in FIG. 7, there is shown a metal U-shaped member which has an upper flat portion and two depending side flanges. Joining the lower portions of the side flanges is a bracing bar which is welded to the flanges to prevent the flanges from spreading under extreme conditions of stress. There is a foam core which is stated to have a density in the range of 4-30 lbs. per cubic foot.
U.S. Pat. No. 3,352,566, and also U.S. Pat. No. 3,416,810, both of which are issued to Kennedy, show arrangements generally similar to that of the first mentioned Kennedy patent noted above.
U.S. Pat. No. 3,498,628, Sullivan, shows a ski where a U-shaped member is formed in a die, heat treated if necessary, and trimmed. A sheet member is attached to the U-shaped member to form a closed rectangular box section with the interior of the same being filled with a foamed plastic material using foamed-in-situ procedures.
U.S. Pat. No. 3,762,734, Vogel, discloses a metal/polymer ski construction. The design includes a pair of generally U-shaped metal channel members disposed in opposed relationship to define a cavity. The channel members are joined along the side walls, and the cavity receives a foamed polymer. The edges of the downwardly depending side walls of the top channel member are flared somewhat and provide edge runners for the ski.
U.S. Pat. No. 3,790,184, Bandrowski, discloses a ski construction where the top and sides of the ski are formed as a metal casing to which is attached generally L-shaped running edges. A pair of polymeric sheets is disclosed between the edges spanning the recess formed by the L-shaped running edges.
U.S. Pat. No. 3,360,277, Salvo, disclosed a ski where there is an inverted U-shaped member with downwardly depending side walls flared outwardly at the lower edges. There is a bottom closure plate joined along the edges as a closure member to provide a generally laterally extending peripheral lip. There is an internal stiffener spanning the transverse dimension between the top face of the U-shaped channel and the lower closure plate.
Also, it is believed that it has been suggested in the prior art to place a steel sheet at the lower surface of the ski and join the steel edges to this sheet. It is believed this is primarily utilized as a means of joining the edge members to the ski. (See, for example, U.S. Pat. No. 2,851,277, Homberg et al.)
While there have been attempts since as far back as approximately sixty years ago (as evidenced by the filing date of May 19, 1924 of the Hunt patent, U.S. Pat. No. 1,552,990) to incorporate metal load bearing structure into the design of a ski, to the best knowledge of the applicant, except for the use of upper and lower aluminum alloy sheets in a sandwich-type construction (as shown in the Head patent, U.S. Pat. No. 3,095,207, and as described previously herein), these various other proposed designs using load carrying metal structure have had at most very limited acceptance (if any acceptance at all) in the ski industry. One can easily speculate, with good justification, that the earlier designs incorporating metal structure were either flawed or impractical, or possibly produced a ski having inadequate performance characteristics. It can further be surmized that as the design and manufacture of skis became more sophisticated over the last several decades, the previously ineffective proposed metal structures appeared to fare only worse by comparison.
Further, the trend in ski design was to obtain improved performance without the addition of weight to the ski, or possibly even a reduction in weight. It was only natural to turn to aluminum, the desirable strength to weight characteristics of which were well proven in the aircraft industry, and later to explore extensively the possibilities of fiber reinforced plastic, which has a yield strength to weight ratio substantially greater (i.e. as much as 30% greater) than metals which might be considered, such as aluminum or steel. Further, as indicated previously, the main design parameters (as mentioned previously, flexural stiffness, torsional stiffness, weight and strength) became channeled into relatively narrow ranges which had been proven to be acceptable to the end user. It is believed that the overall trend of this evolution of ski designs has had the effect, as it often does with many technologies, of channeling or narrowing the design efforts along certain known avenues.
Another factor which has affected the evolution of ski designs and manufacturing methods is that much of the valuable information affecting the ski design is highly proprietary to the various ski manufacturers. Much of the data concerning desired performance characteristics and design parameters to achieve such characteristics is derived by empirical methods. Further, as a practical matter, the ultimate test of the quality or excellence of a ski, in terms of consumer acceptance, depends upon its actual performance in various snow conditions, with regard to such things as the stability of the ski in straight downhill travel, how effectively the ski engages the snow in a turning maneuver so as to execute the turn with the least amount of lateral slippage and within an adequately small turning radius, etc. Certainly, the evaluation of physical characteristics of the ski which can be quantified (e.g. flexural and torsional stiffness, weight and strength), as well as the design of the ski relative to these and other characteristics, remains something of an art. Thus, while there has been some published material on ski designs, there are not in the published literature widely accepted and well defined guidelines dictating the specifics of ski design with any great precision. Rather, there are pockets of closely guarded expertise in the refinements of ski design which have been withheld from becoming part of the prior art relating to ski design.